解读过滤器(Filter)和拦截器(Interceptor)的使用

chain.doFilter(request, response);这个方法的调用作为分水岭。事实上调用Servlet的doService()方法是在这个方法中进行的。

@WebFilter(urlPatterns = "/*", filterName = "myFilter")
public class MyFilter implements Filter {
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化代码
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
                         FilterChain chain) throws IOException, ServletException {
        // 前置处理
        System.out.println("Before Filter");
        
        // 执行后续过滤器或Servlet
        chain.doFilter(request, response);
        
        // 后置处理
        System.out.println("After Filter");
    }

    @Override
    public void destroy() {
        // 销毁代码
    }
}

<filter>
      <filter-name>filterDemo1</filter-name>
      <filter-class>com.thit.filters.Filter1</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>filterDemo1</filter-name>
      <url-pattern>/*</url-pattern>
      <!-- /*是对所有的文件进行拦截 -->
  </filter-mapping>

//拦截器1
public class LoginInterceptor implements HandlerInterceptor{
	
 
	//预处理1.程序先执行preHandle()方法，如果该方法的返回值为true，则程序会继续向下执行处理器中的方法，否则将不再向下执行。
	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		// TODO Auto-generated method stub
		System.out.println("1:拦截器1,程序进入preHandle方法");
		User u=(User) request.getSession().getAttribute("user");
		if(u==null) {
			System.out.println("在进入方法之前判断session的用户是否为空！");
			System.out.println("地址："+request.getContextPath());
			//http://localhost:8080/login
			response.sendRedirect(request.getContextPath()+"/login");
			return false;
		}
 
		return true;
	}
	//后处理 	2.在业务处理器（即控制器Controller类）处理完请求后，会执行postHandle()方法，然后会通过DispatcherServlet向客户端返回响应。
 
	public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
			ModelAndView modelAndView) throws Exception {
		// TODO Auto-generated method stub
		System.out.println("2:拦截器1,程序进入postHandle方法");
		
	}
	//完工之后 	3.在DispatcherServlet处理完请求后，才会执行afterCompletion()方法。
	public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
			throws Exception {
		// TODO Auto-generated method stub
		System.out.println("3:拦截器1,程序进入afterCompletion方法");
		
	}
 
}

@Configuration
public class WebConfig implements WebMvcConfigurer {
    
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new MyInterceptor())
                .addPathPatterns("/**")  // 拦截所有路径
                .excludePathPatterns("/login"); // 排除登录路径
        
        // 可以添加多个拦截器
        registry.addInterceptor(new AnotherInterceptor())
                .addPathPatterns("/admin/**");
    }
}

<mvc:interceptors>
    <mvc:interceptor>
        <mvc:mapping path="/**"/>
        <mvc:exclude-mapping path="/login"/>
        <bean class="com.example.MyInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>